La plante d’intérieur est dans le cache-pot.

French nouns have grammatical gender, so each noun normally takes either a masculine or feminine article.

• plante is feminine, so it takes la
• cache-pot is masculine, so it takes le

That is why the sentence has:

• la plante
• le cache-pot

This does not mean the plant is female and the pot is male. It is just a grammar category.

In plante d’intérieur, d’intérieur means something like for indoors or indoor.

So une plante d’intérieur is an indoor plant / houseplant.

Literally, it comes from de + intérieur, giving the idea of a plant for the inside/interior.

Because French uses elision: when de comes before a word beginning with a vowel sound, the e drops and becomes an apostrophe.

So:

• de + intérieur → d’intérieur

This is very common in French:

• de + eau → d’eau
• de + accord → d’accord

Because d’intérieur is not working like a regular adjective directly attached to plante.

In plante d’intérieur, the structure is:

• plante
  • de/d’
    • intérieur

So it is more like plant for the indoors/interior, not interior plant in the usual adjective-agreement sense.

That is why intérieur does not change to intérieure here.

You might be understood, but une plante d’intérieur is the normal and idiomatic expression for houseplant / indoor plant.

So for a learner, the safest choice is:

• une plante d’intérieur

rather than:

• une plante intérieure

A cache-pot is a decorative outer pot that hides the regular plant pot inside.

So it is not always the same as a basic pot de fleurs.

A useful distinction is:

• pot = pot
• cache-pot = decorative cover pot / outer pot

So the sentence means the plant is in the outer decorative pot, not necessarily planted directly in it.

Because cache-pot is a fixed compound noun in French, and it is conventionally written with a hyphen.

French has many compound nouns like this. The hyphen is just part of the standard spelling.

So you should learn it as one vocabulary item:

• un cache-pot

Dans means in / inside.

Here it is used because the plant is physically inside the cache-pot:

• La plante est dans le cache-pot.

That is the normal preposition for being inside something.

Est is the il/elle/on form of the verb être (to be) in the present tense.

The subject here is la plante, which is singular and equivalent to it in English, so French uses est:

• la plante est = the plant is

Other present-tense forms of être are:

• je suis
• tu es
• il/elle est
• nous sommes
• vous êtes
• ils/elles sont

A natural pronunciation is approximately:

la plant dan-tay-ree-ur eh dan luh cash-poh

A few notes:

• plante ends with a nasal vowel; the final t is normally silent
• in d’intérieur, the d’ links smoothly into the next word
• est is pronounced eh
• cache-pot ends with a pronounced pot sound, roughly poh

You do not need to pronounce every written consonant.

Not really a required one that beginners need to worry about.

The main smooth connection is in:

• d’intérieur

because the apostrophe forces the words together.

But you would not normally make a liaison like this:

• est dans

So just read it naturally:

• La plante d’intérieur est dans le cache-pot.

It becomes:

• Les plantes d’intérieur sont dans les cache-pots.

Changes:

• la → les
• plante → plantes
• est → sont
• le → les
• cache-pot → cache-pots

So the sentence still keeps the same structure, just with plural forms.

The structure is:

• La plante d’intérieur = subject
• est = verb
• dans le cache-pot = prepositional phrase showing location

So the pattern is:

[subject] + [être] + [location]

This is a very common and useful French sentence pattern.